The easiest way is to get VideoReDo. That will allow you to edit out the parts of the show you don't want and convert the .tivo files to .mpg quickly and simply. You can then join clips from separate shows together to make a longer video. You can then use the Tivo Desktop, pyTivo or KMTTG to copy the new video back to the Tivo.

If that is all you want to do you can just get the $50 version of VideoReDo. If you want to make DVDs from your Tivo videos you will want the Suite version.

For more elaborate tasks, you probably want a video editor; but to cut out a single clip, these are the two methods I've been using lately:

1. If you have at least two TiVos: Advance the recording to what you want as the start point. Pause it there. Move to the other TiVo, and select "Transfer from paused point". Stop the transfer when you reach the desired endpoint. You can then move the truncated recording back to the other TiVo, or to your computer.

2. Download and decrypt the whole program. Play it back, and take note of the desired start and end points (or do this on the TiVo). Then, use FFmpeg to copy the desired portion:

This would take a five minute clip, starting an hour into the recording. If the result isn't quite right, you can tweak the numbers and repeat, down to tenths of seconds if necessary. You can also use the TiVo-to-TiVo method to do the initial editing, and fine-tune it with the FFmpeg technique.

If you have 2 TiVo's pause playback of the program at the start of the section you want then from the other TiVo start a transfer from the pause point watch and FF as needed then stop the transfer at the end of the section.